FIGS. 3(a) to 3(d) are sectional views showing process steps for partially producing high resistance regions by proton bombardment in a conventional method for producing a semiconductor laser device, disclosed in pages 726 to 728 of PROCEEDINGS OF THE IEEE (JUNE 1972). In these figures, reference numeral 1 designates a semiconductor substrate, reference numeral 2 designates a mask material, reference numeral 3 designates a photoresist, reference numeral 4 designates protons, and reference numeral 5 designates high resistivity regions.
A description is given of a conventional proton bombardment with reference to FIGS. 3(a) to 3(d).
First, a mask layer 2 comprising an metal such as gold or titanium or an insulating material such as SiO.sub.2 which obstructs the proton bombardment is formed on a semiconductor substrate 1 by such as a vacuum evaporation (FIG. 3(a)).
Then, a stripe-shaped photoresist 3 is formed on the mask layer 2 using photolithography technique (FIG. 3(b)).
Then, a strip-shaped mask for proton bombardment 2a is formed by a selective chemical etching using the photoresist 3 as a mask (FIG. 3(c)). Here, buffered hydrofluoric acid can be used as etchant in either case where the mask layer 2 comprises a metal or an insulating material.
Next, protons bombard the substrate 1 using the mask 2a to induce high resistivity regions 5 (FIG. 3(d)).
FIGS. 4(a) and 4(b) are sectional views each showing a semiconductor laser device having a light guide produced by different refractive indices of adjacent layers and a current confinement structure produced by proton bombardment, disclosed in "Appl. Phys. Lett. 38 (11)". In these figures, reference numeral 11 designates an n type GaAs substrate. An n type Al.sub.0.3 Ga.sub.0.7 As cladding layer 12 is disposed on the GaAs substrate 11. An n type or p type or undoped GaAs active layer 13 is disposed on the cladding layer 12. A p type Al.sub.0.3 Ga.sub.0.7 As cladding layer 14 is disposed on the active layer 13. A p type GaAs cap layer 15 is disposed on the cladding layer 14. Reference numeral 16 designates an active region.
In FIG. 4(a), the position of mask 2a is deviated from alignment with the stripe portion constituting the active region 16. On the other hand, in FIG. 4(b), the position of mask 2a is aligned with the stripe portion 16. In order to align the position of mask 2a with the stripe portion 16 as shown in FIG. 4(b), high precision is required for the superposition in a photolithography process. When the high resistivity regions 15 deviate from the stripe portion 16 as shown in FIG. 4(a), fatal performance degradation, such as deterioration in linearity of light output vs. current characteristics of the semiconductor light emitting device, occurs.
In the above-described conventional production method, a high precision alignment for the mask 2a is required, and variations in the alignment cause also variations in the element characteristics.